Predication of Shoreline Migration in Storm Condition with N-line Model

This study introduces an N-line model for predicting short-term beach changes during storm condition and its effect on the long-term shoreline migration. Previous models, e.g one-line model are not very successful for estimation of beach changes due to storm, because in their formulation, the shoreline migration was assumed to be produced mainly by the longeshore transport and the cross-shore transport was canceled over a long period. N-line model has the advantage of accounting for the cross-shore transport effects, such as storm - induced erosion and cyclic shoreline changes due to wind-wave climate. Storm condition, which prevails several weeks intermittently during winter in every year, induces a large amount of bed sediment motion to offshore direction. Therefore, a sever beach changes occurs during every winter and it is consequently play a significant role in the long-term evolution of the shoreline changes. In particular, at Japan Sea, field observation indicates that wind storm induces a very strong undertow current that enhances from surf zone to offshore zone: it acts as the main agent of moving sediments to offshore region. Besides, has revealed the significant role of the storm effect on nearshore hydraulics of Japan Sea. In this paper the model applicability to predict short-term beach evolution and its effect on large-term shoreline migration is demonstrated with an illustrative example at Ogata Coast in Japan Sea.